A needs index for mental health care in England based on updatable data.

BACKGROUND: Mathematical models relating rates of mental health care use to population characteristics such as social deprivation are widely used in both planning and researching mental health services. The models currently in wide use in England are based on data mostly derived from the 10-yearly population censuses. These are perceived to be out of date many years before new census data are available for their replacement. A new set of government deprivation monitoring statistics based mainly on annually updatable data has recently been developed. This study set out to produce a mental illness needs index based on these new data.
METHODS: A series of regression models were tested using individual domain scores from the DETR Index of Multiple Deprivation and the Office of National Statistics area-type classification as independent variables to predict 1998/9 psychiatric admission rates for broad diagnostic groups for 8251 of the 8414 electoral wards in England as dependent variables.
RESULTS: The distribution of admission numbers in wards showed a pattern of over-dispersion with an excessive number of zero values for conventional regression approaches. A two-stage 'hurdle' model was, thus, adopted, predicting first the likelihood that wards would produce any admissions and second the probable number. This produced satisfactory predictive power, with residual variance showing strong geographical patterns associated with administrative areas, probably arising from differential resourcing or idiosyncratic clinical practice.
CONCLUSIONS: A website providing data on the various indicators has been provided and its uses are indicated.